1. Field of the Invention
The present invention relates to semiconductor devices and their manufacture, and more specifically to a structure and process integration for a flash storage element and dual conductor complementary field effect transistors.
2. Description of the Related Art
Electrically blowable fuses can be incorporated in very large scale integration (“VSLI”) integrated circuits, i.e., semiconductor chips having a multiplicity of conductively interconnected transistors thereon. Such fuses typically store state information used to program circuit functions of the integrated circuit. FIGS. 1A-B illustrates an electrically blowable fuse 10 of a type which is commonly provided within VLSI integrated circuits. Fuse 10 is blown when a sufficiently high programming current is caused to flow across a narrow “fuse link” of conductive material between the anode and the cathode. When the programming current is applied to the fuse, electromigration causes the more highly conductive silicide material of the fuse link to retreat away from the less conductive underlying polycrystalline (Poly-Si) silicon region. After programming, the electrically blowable fuse is in a highly resistive state which can be detected by a circuit associated with the fuse.
One advantage of the electrically blowable fuse 10 is that it has a structure similar to a gate of a field effect transistor (“FET”). Fuse 10 can be fabricated simultaneously with the FETs of an integrated circuit without requiring separate masks and without requiring separate processing steps to be performed to form the fuse.
The structure of the electrically blowable fuse 10 is similar to a traditional gate of a FET in that it has a semiconductor region “Poly-Si” at the lower major surface 12 of the fuse 10 in contact with an underlying dielectric region “STI-Oxide”. However, the electrically blowable fuse 10 has a very different structure from a metal gate of an FET. In a metal gate, a metal layer extends along the lower major surface of the gate in contact with the gate dielectric. If the metal layer were incorporated in the electrically blowable fuse 10, the fuse would not function because such metal layer would remain in place after programming and would remain conductive. Accordingly, there is no conventional process for simultaneously fabricating electrically blowable fuses and metal-gated FETs without requiring separate processing steps to form the fuses.